1. Field of the Invention
The present invention relates to heat treatment apparatus and method for heating substrates, such as semiconductor wafers or glass substrates for liquid crystal displays, by irradiation thereof with light.
2. Description of the Background Art
In general, lamp annealers using halogen lamps are conventionally used in the process for the ion activation of ion-implanted semiconductor wafers. Such lamp annealers activate ions in semiconductor wafers by heating (annealing) semiconductor wafers to temperatures of the order of, for example, 1000 to 1100° C. Such heat treatment apparatuses raise substrate temperatures at rates of the order of several hundred degrees per second, using the energy of light emitted from the halogen lamps.
Meanwhile, recent progress toward a higher integration of semiconductor devices increases the need for shallower junctions with decreasing gate lengths. It is however known that, even though the ion activation of semiconductor wafers is carried out using the aforementioned lamp annealers that raise the temperatures of semiconductor wafers at rates of the order of several hundred degrees per second, a phenomenon can still occur in which implanted ions, such as boron or phosphorus, in semiconductor wafers are deep diffused by heat. The occurrence of such a phenomenon raises a concern that junctions might get deeper than desired, thus hindering good device formation.
With this in view, U.S. Pat. Nos. 6,998,580 and 6,936,797 disclose the techniques for irradiating semiconductor wafer surfaces with flashing light emitted from xenon flash lamps so that the temperatures only on the surfaces of ion-implanted semiconductor wafers rise in a very short time (several milliseconds or less). The xenon flash lamps have a spectral distribution of radiation in the range of ultraviolet to near-infrared regions and have shorter wavelengths than conventional halogen lamps; the range of their distribution almost agrees with the fundamental absorption band of silicon semiconductor wafers. Thus, the flashing light emission from the xenon flash lamps to semiconductor wafers will produce only a small amount of transmitted light, thereby allowing a rapid rise in the temperatures of the semiconductor wafers. It is also known that the flashing light emission in a very short time of several milliseconds or less causes a selective rise in temperature only in the vicinity of the surfaces of semiconductor wafers. Thus, the very-short-time rise in temperature with the xenon flash lamps achieves only the ion activation without causing deep diffusion of ions.
The high-energy ion implantation during the ion implantation process prior to the flash heating process, however, results in generation of a number of defects in silicon crystals on semiconductor wafers. The very-short-time temperature rise with the xenon flash lamps achieves the ion activation, but it will not eliminate the defects generated.
Further in the heat treatment apparatuses with the xenon flash lamps, instantaneous irradiation of semiconductor wafers with flashing light with extremely high energy causes an instantaneous and rapid rise in the surface temperatures of semiconductor wafers. This undesirably causes sudden thermal expansion of the wafer surfaces, resulting in cracking of the semiconductor wafers.